Object locator system



Jan. 9, 1951 w. F. KANNENBERG ETAL 2,537,139

QBJECT LOCATOR SYSTEM Filed July 14, 1944 2 Sheets-Sheet l FIG.

TR. 50X

056/ OSCOPE TRANJMITTER RECEIVER 1 own/0125,94)

W F KANNENBERG .1 ,9 K/IVZER INVENTORS- a m SCHRAMM ATTORNEY I? K/NZER ATTORNEY w I: MAINE/vanes .1 c. n! SCHRAMM 6. WILSON i 1 2 Sheets-Sheet 2 fNl/ENTORS Jan. 9, 1951 w. F. KANNENBERG ETAL OBJECT LOCATOR SYSTEM Filed July 14, 1944 Patented Jan. 9. 1951 UNITED; STATES PA EN r,

OBJECT Q AZEDK-SY TEMQ' Application aiuly 1451944, Serial N0. 544,990-

s lai1ns. -=;(Cl. n er) This invention relates to 1 apparatus Pand systems -for testing object'locators of the type in which the position and' distance of remote-ob ject are ascertained from 'the echo interval :aof reflected electromagnetic waves;

Object locators --employing electromagneticwaves commonly transmit pulses of high j frequency waves, forexample, pulses. of the order of a microsecond in: length comprising wavesof the order of IO-centirrietenWavelength. i At thetermination of *each transmitted pulse; a sensitive radio receiver which'was disabled or the sensitivity of whichf-was reduced' during tranS- mission of a pulse is again placeddn sensitive re ceiving condition.- A cathode ray oscillograph associated with the-- radio' receiverserves -'to lineate a time graph showingthe instant of termination of the transmitted pulseand the in-.: stant of reception of theenergy reflectedbacka from the remote 'obiect and detected by the re ceiver. The cathode'ray oscillograph is usually-' provided with a scale-to give -a direct-measureof the" echo interval and-it maybe-caIibratedtQ- show the distance to the reflectedobjecti-n miles a or yards.

Many factors determine the eflzectiveness oi such an object locator-system;"Amongtheseare coincidence oftuning between the transmitter and the radioreceiver. At wavelengths .such as' indicated and with object-locating apparatussimple and compact enough for mounting in air-; craft, it is quite possible for the transm-itte'r and; receiver to =getout of tuning alignment-in con sequence of the violent'changes which =occurin temperature and other characteristics of theambient atmosphere.-- If the detectingelement: of the receiver or any other'component ofthe receiver or of the transmitter should deteriorate in performance the over-all effectiveness of the system will diminish, -In some systems-in which it in such a way as to give evidence of such-5oi failures.

Another object of the invention is ;to enable thereceiver of anwbject locator to =be ;readily tuned to the transmitter;-

For thepurpose of enablingthe receiver or an 66? mitted electromagnetic waves.

2 object locator tobe tuned to its associated transg mitter there has been previously, proposed what maybetermeda reradiating chamber resonator Such :a reradiating resonator is provided witha small pick-11p antenna tolead energy into. the

resonanceschambert during remission-of a pulse from-the transmitter of the object locator. a As, long as the impulseepersists the resonance cham- -Y; bercabsorbs energy and builds, up an'vinternal;

electromagneticufieldpthe final intensity of which ifroma reflecting body except-thatwthere is nos;

echo-interval; .7 ASBIOIIgHS the chamber continues; to -giveout sufiicient energy to override the-res, ceivera noise the significant indication at the; cathode-"ray oscillograph of the receiver persists... In the parlance ofcthis art and from analogy to. theoperationaof bells; and tuning forkssthe resonance chamber is said-toefring" and theine terval measured -from-the cessation of the transmitted impulse up to theinstant that the elec-. trical echo received at the receiver is, in efiect," overridden and obliterated on the cathode rayoscillograph-indicationby the receiver! noise is known as the ring-time oi the reradiating: resonance chambers Since the intensity ofthe originally transmitted impulse, the resonance" frequencyof the reradiating chamber, the Q01; resonance persistence of the chambenthe tuning; of the-receiver-and the sensitivityof the detector all are factors in the end result, the ring time: of-such a test-system is an lexcellentnindex. .of the over-all effectiveness of :the. object ilocator or radar system test.

Theintervalsiinvolved in the operation of such. a reradiating chamber test'system are-brief and: the selectivity of the chamber and oftheradio receiver is high. r It is; therefore, no easy matter to ascertai'n in what directionchanges -must be made to bring the various-devices into tunin agreement.- a

An object of this invention is tomake the na-- ture of thenecessary corrections readily apparent. 1

Conditions may change-quickly thus requiring a readjustment of tuningperhaps during flight ofan-airplane on *which the test apparatus islocated. Another object is to enable the necessary determinations to be made with simple apparatus requiring a minimum of time.

It is, of course, most important to be able to know when the various elements have been ad-. justed to the point of maximum effectiveness of the system and to know how the effectiveness of the apparatus, when so adjusted, compares with the maximum performance of which it has been shown to be capable. An additional object of the invention is to indicate when correct frequency alignment has been attained and to enable the over-all effectiveness of the object locator to be quickly measured.

In accordance with the invention, the resonance frequency of the reradiating chamber is varied cyclically and continuously by a motor which causes the resonance frequency to sweep pulses of electromagnetic waves and measures the time interval thereafter before receipt of the reflected pulses arriving from a remote reflecting object. The object locator comprises a radio transmitter I and a radio receiver 2 connected to a radiating element 3 through an apparatus 4 commonly known as a TR box. Associated with the radio receiver is a cathode ray oscilloscope 5.

The transmitter may be of any well-known type as, for example, a magnetron capable of transmitting high power pulses of high frequency electrical oscillations. In a practical apparatus over a given frequency range, which includes the 7 number of pulses or wave trains of high frequency waves. The reradiating chamber stores up energy during the pulse and upon termination of the pulse reradiates some of its oscillation energy back to the receiver so that the cathode ray oscillograph device connected to the receiver of the object locator gives a corresponding reflected pulse indication which varies in magnitude with the ring time of the reradiating chamber. It is apparent that the transmitter frequency will lie in the region near the reflected pulse showing the highest ring time indication and, in general, between the highest two such indications. The reradiating chamber is also provided with manual means to permit adjustment of its midsweep frequency to be made during operation offthe motor driven tuner. It is accordingly possible to ascertain in what part of the cyclically traversed tuning range of the reradiating chamberv the frequency of the transmitter falls and to make the requisite tuning corrections to align the tuning of the transmitter and the reradiating chamber. After the reradiating chamber and the transmitter are in frequency agreement the various other components of the radar system may be adjusted one by one to secure a final maximum overall performance as indicated by the ring time indication on the cathode ray oscillograph screen.

. Finally, in order to avoid any distortion of the normal field of the transmitter which might tend to give an erroneous indication from the refiected energy, it is desirable to provide arrangements which will minimize the field distorting tendency of the resonant cavity apparatus and its pick-up at times when the transmitter is not being tested.

It is another object of the invention to efiectively disconnect at will the pick-up from the resonant cavity so that the pick-up will not present a load or energy-absorbing characteristic to the transmitter field.

In the drawing:

Fig. 1 illustrates schematically an object 10- cator test system in accordance with an embodiment of the invention.

Fig. 2 is a top plan view of the motor-tuned electrical resonance chamber of Fig. 1;

- Fig. 3 illustrates in perspective the fundamental parts of the reciprocating drive mechanism of the tuner of Fig. 1.

Referring to Fig. 1 there is shown schematically an object locator of the type which transmits the peak power of the transmitted pulse may be of the order of 25 to 50 kilowatts. The pulse may be of the order of a microsecond, in length and the oscillation wavelength may be of the order of one-half centimeter to 30 centimeters. These magnitudes are not given in any sense as limitations but merely as examples of practical values which may be employed.

The TR box may be of the type disclosed in application Serial No. 474,122, filed by A. L. Samuel, January 30, 1943, relating to transmitting and receiving circuits for Wave Transmission Systems. The TR box connections may comprise a wave guide connected between the transmitter and the receiver on the one hand and the radiator 3 on the other, so as normally to provide a ready path for incoming electromagnetic waves from the radiator 3 to the receiver 2. When the transmitter l impresses high power oscillations upon the TR box l, an electrical discharge device therewithin breaks down placing such very low impedance across the input to the receiver 2 as to efiectively desensitize the receiver. The oscillation energy is, accordingly, impressed upon the radiator 3 and is transmitted out therefrom into space in a direction sharply defined by the polarization of the radiator 3 and the configuration of the surrounding parabolic reflector 6. Upon cessation of the impulse, the TR box returns to its normal condition and restores the sensitivity of receiver 2 so that at the time that the outgoing impulse has travelled to the refleeting object and the reflected impulse has arrived at the radiator 3, the receiver will be in condition to receive and indicate it.

The cathode ray oscilloscope may be of wellknown type in which the indication is portrayed in the form of a trace, the vertical coordinate of which is proportional to the intensity and the horizontal coordinate of which represents elapsed time as-measured by a sweep circuit in wellknown manner. There is shown on the cathode ray oscilloscope a typical diagram in which the ripple portions marked N represent noise fluctuations in the absence of substantial signal. I represents the transmitter impulse and the portion RI extending over the time duration designated as T represents the reflected impulse. This graph will be discussed more fully following the disclosure of the test equipment.

The effectiveness of an object locator equipment of the type schematically represented by elements I to 5 inclusive, is, in large measure, dependent upon the skill of the operator in keeping his set in tune and on his early recognition of trouble. Particularly is this true of shipsearch apparatus or air-borne apparatus operating over Water. In such cases, the screen of the cathode ray oscillograph is sometimes blank for'long periods. The spotting of a real target at intervals gives an opportunity for retuning and if it be a distant target provides some measare of the rangecapabilities of the object loca.

Underiactual, field: conditions; the :obj ect locat is 'generallyi not energized untilcthez plane -,is in therair and sometimes it remains unenergized-for;

as longras twenty :minutes or. more after-41a take-u Ofiw By -this time no targets maybe available Talld: what is rmorei important, evenwif the transmitter and: =receiveri were originally: in: :tune nonrsthe; ground they: --may:-drift 1 apart as:theyuheat v up;

unless held in control "by automatic sfre uencyu L COHtI OL Without .targets the .operator cannot;

kno'w whether or not this has occurred. :i Hence unless-:he has a targetvavailable-hisschance that the-receiver will stay in tunelwith .the trans-m mitter over-a long trip is doubtful =whether --.he

tries-to retune or note Sometimes the sea, ,it- H sel-f', '-:can--be--used--as a reflector. for tuning but it is not always satisfactory;

Another field condition occurs inretuning the receiver to pick up a beacon targetwhich mayhappen to be-availableand then trying to return to the-original searching tuning point; It should; of course,- be unnecessary to change the receiver settingfor the two conditions if it has-been-accurately enough made-and if no changes'in' the I environment have taken placebut in thefield the necessary adjustments of the object locatorcannot alwayshe --made accurately enough so I that this is possible. It will be apparent, therefore; that it is highly desirable to have'a depend able target orrei lector-which may be fully under- It is to v Thetest equipment for picking up energy-of the object locating pulse, storing it and returning some of the energy after the cessation of the pulse-to the object locator receiving equipment may comprise an energy pick-up device such as the-dipole *8 placed at the-focus of parabolic refie'ctor-Q and connected by the coaxial transmission line H] to a coupling element H projecting through an aperture in the lower wallof an elcctrical resonance chamber i2 into the interior electromagnetic field spaceof thechamber, The coupler lI rnay-comprise a small loop, the ter-- minals of which are connected between the central and-the outermonductors of the coaxial pair with :theloop projecting slightly within the interiorspace of the chambeix The resonance chamber l2 comprises -a cylindrical cup-shaped body portion having a tightly fitting cover 13 bolted thereto as at it. Also coupled tothe electrical resonance chamber through a normally retracted coupler 15 aligned'withan aperture H5 in the bottomof the chamber is a-coaxial output circuit 1'! connected through a series rectifier-i8*- witha, shuntcondenser. IQ anda microammeter wi -With the source 48 and solenoid 3|; the'solenoid 20::The coupling loop l5 and the end of the coaxial line I! to whichit is connected-are mount- 8d--With a, connector terminal block Zl slidablir mounted: in a vertical guicleway within-the frame zzn tt h mt th lower t u .surface of 7Q1l10id remains energized and the rod40 is ins-con-ss chamber l2. The connector block 2| is provided a with a cylindrical extension 23- and a retractile springz lasurrou-nding the cylindrical extension and reacting betweena flanged head thereon andr 6 a downward: position nth-us :aetracting: thezooupleriw l5: :fronrothe interior i-spacecof the:.= resonance: 1 chamber-112.? Connectonblock- 2llcarries a lat x; erallyrprojccting threaded stud 25:?which extends throughia slot inathe frame-ZZAandcarriesia winger nut. 2 e i to enable it to be clam ped J thus -holding t;- the connector block- 2 l fandthecoupler, i SAin any desired position. t It is, accordingly, possible byw freeing ivi'ng -nutit to.permit thetspring Mt-toe retract the coupler or if a'desired,thecylindricalic extensionv i 23' may be pushed -upwardlyxagainstas the" action of: the springv to carry-the coupler i 54 intogthe cavity whereupon wing nut: ZS may-be employed to lock the terminalblock in-that posi tion In order :to cause the resonance trequencya of-the "chamber l2 to be varied cyclically over a r desired range the chamber is provided-with an interior pistonrlike disc 28'-near itsupper end: Th'episton is supported and is causedte recip rocate in a verticaldirecticnby ansof -a mechanism mounted on the cover-' fr ne t-3 including an upstanding frame 29; a hollow. cyliri dri'cal guide 39 and a vertically-disposed electrical-1 solenoid 3|, each rigidly attached to -the covere Mounted on the back of frame membeniES Wi-th itsdriving shaft projecting therethrough in -a horizontal direction, is'a small electrical moton 32norma1ly-operating at a speed of the -ordenofw 750 revolutions per minute.- Connected-to-theend of the driving shaftofmotor-32 m a cam member 33; The piston 28 is attachedby means of a screw 3 to a piston rodtd supported by-a flexible fiatstrap 35 of Phosphor bro nze-Whichw as-shown. in Fig. 3, extends over a roller 37 andterminates in a fixed connection on-the drurn-38u Alever system, best shown in Fig.=':-3,= comprises a rigid rectangular metallic rod lll projecting into a block ll which is pivotally-'mount'-- ed on the frame 29 by means of the pivot rod- 42%: Block 4| has attached thereto at :its upper surface a long leaf spring member 453, the endof; which projects through a slot in the plunger 44 of solenoid 3| beneath a shackle pin 45. r In the unenergized condition of solenoid 3| the piston rod 35 is drawn inwardly under the influence 01* helical spring 46 surrounding the piston rod 35%?- and extending between the tuning disc-28 -and=-'--: the interiorsurface of the cover l3; 4 The posi- 'tion of the piston rod SB-is limited in a downwarddirection by the leaf spring 43,"-the-outer-'-- end of which bears against pin 45. In this extremeposition of the tuning piston 28 rod 40 is entirely-disengaged from cam 33, the interior: volume of the resonance chamber is at a minimum and its resonance frequency is so much higher than an frequency which transmitter l may have that the resonance chamber does not respond-to the pulses received bypick-upelement 8 from transmitter l.- Accordingly,-theaction of the spring ifi is to maintain the -test equipment at such a different frequency than the oscillations of the transmitted pulses that it is efiectively disconnected from the trans-=- mitter. Upon closure of the key 47 in series attracts its plunger 14: downwardly'to rock levers system 43-,"4I; so about its pivot 42 to bring the rod 401mm contact with the cam 33% is illus trated in Fig. 1. Thereafter as long as the soletact v with t the cam 33 the camv will-perve ted cyclically depressthe rod by swinging the levers; system about its pivot 42: against the-r'flexing resistance of the spring 43 thus causing the'-rolltheframedz to drawthe connector blockzl intomwaercl to correspondingly fall and rise-andso oscillating the piston tuner 28 in a vertical direction. The apparatus is preferably so designed that the range of resonance frequencies of chamber l extending from that corresponding to the lower position of the tuner piston 28 to that corresponding to the high position includes the entire gamut of frequencies through which transmitter I may possibly be varied. In order to shift the band of frequencies of the resonance chamber the revoluble drum 38 is provided with an attached adjusting arm 98 carrying at its upper end a set-screw 99 by which it may be locked in position at any points on the periphcry 50 of an arcuate extension of an upstanding side wall It will be apparent that rotation of the arm 93 in a counterclockwise direction will lower the central position of the tuner piston 28 and rotation to the right will conversely wind up the flexible strip 36 about the drum 38 and raise the central position of the tuner piston. Moreover, this adjustment of the central position may be made while the tuning apparatus is being oscillated by the action of cam 33 on the rod 40.

If the object locator apparatus of Fig. l is installed on an aircraft the testing equipment may be mounted on the same aircraft with the pickup antenna 8 in position to receive energy from the antenna 3 of the object locator transmitter. In its normal inact ve condition the test equipment is so far detuned from the test pulses of the object locator transmitter that it will be effectively insensitive to them. Accordingly, when the object locator is put into operation the test equipment in no way afiects it. When it is desired to use the test equipment to check the performance of the object locator the operator closes the circuit of the solenoid 3| and simultaneously closes the circuit of the motor 32. For this purpose solenoid 3| and motor 32 may be connected in the same circuit. Operation of the solenoid 3| brings the tuning of the chamber 12 to a frequency in the neighborhood of that of the transmitter and operation of the motor 32 serves through cam 33 and the lever system 40, 4|, 42, 43 to cyclically vary the resonance frequency of the resonance chamber 1 2 through a band which includes the frequency of transmitter I. At some point in its cycle a natural resonance frequency of the resonator l2 will agree with the frequency of the transmitter l and the pulse of oscillations sent out from transmitter antenna 3 will be picked up by element 8 and caused to build up a strong electromagnetic field within the chamber l2. Simultaneously the outgoing pulse from transmitter the receiver, nevertheless, indicates the pulse as at I on the screen of oscilloscope 5 since the energ of the pulse is so very high. Upon ces sation of the pulse at the beginning of the interval T the strong electromagnetic field which has been built up by resonance within the resonance chamber I 2 delivers energy to the pickup element 8 from which it is radiated outwardly to simulate a reflected pulse. This energy received by antenna 3 is impressed through the TR box 4 upon the receiver 2 and is indicated as a reflected pulse RI. The receiver 2 which had been desensitized during transmission of the high energy pulse quickly regains its normal sensitivity. Returned energy continues to cause an indication of the cathode ray oscilloscope 5 until, as it rapidly falls away at the end of the period T, the trace disappears in that of the noise N. The period T measured from the termination of the initial high power pulse to the time when the reflected impulse efiectively disappears is known as the ring time of resonance chamber 12. It may be increased by enhancement of any factor which has to do with the quantity of energy returned by the test equipment to the receiver 2. Among these factors are the power and the wave shape of the initially transmitted pulse. The transmission factor of the transmitting antenna and its associated circuits and likewise of the test antenna 8 and its associated coaxial circuit ID are important. Any adjustment of this equipment which augments the amount of transmitted energy or of that returned increases the ring time T. Of very great importance is the resonance persistence or Q of the resonance chamber I2 and the coupling of the loop H with the electromagnetic field of the resonance chamber. In order to make the ring time as long as possible, or what leads to the same result, to increase the effectiveness of the test equipment it is desirable to reduce the transmission loss in the coaxial line It] as far as possible. This consideration leads to placing the pick-up element in a position where it is exposed to the transmitter field and placing the resonance chamber [2 in a position close to its pick-up element 8 and hence in the nose portion of the airplane 01' whatever part carries the radiator 3 of the object locator. It is for that reason that a remote control of the test equipment is desirable.

The resonance persistence or Q of the resonance chamber 12 may also be increased by increasing the conductivity of its interior surface as, for example, by a coating or plating 27 of silver on the interior surface of the piston and of the cylindrical wall and the end wall opposite the piston. The chamber 12 and the piston may consist of brass, copper, aluminum or any other good electrical conducting material or of any good structural material which will serve as a supporting medium of adequate rigidity and strength where the material is provided with a coating of electrically conducting material of high conductivity on the interior surface of the chamber and piston.

The apparatus may also be used on the ground or elsewhere as a simple wave meter. For this purpose, the cylindrical extension 23 may be pressed upwardly and locked in position by the wing nut 26 thus bringing the coupler l5 into the interior field space of chamber I2. The tuner piston 28 may then be manually manipulated until a maximum response is noted on the direct cru'rent meter 20 and the frequency determined by any suitable calibration of the position of the chamber being movable, a motor-driven means for producing an eccentric motion, a support,

lever means pivotally mounted upon said support and connected to said chamber end, said lever engaging said eccentric motion-producing means for translating said eccentric motion into a reciprocating motion of said end to periodically vary the resonance frequency of the chamber,

and remotely controlled means to efiectively disengage said lever from said eccentric motionproducing means at will and to simultaneously shift said end to such a position that the natural resonance frequency of the chamber falls outside the range through which the resonance frequency may be periodically varied.

2. A testing system for an electromagnetic echo object locator comprising a resonator having a substantially closed cylindrical conducting chamber adapted for resonance to high frequency electromagnetic oscillations, one end of said chamber being movable, a motor-driven means for producing an eccentric motion, a support, lever means pivotally mounted upon said support and connected to said chamber end, said lever engaging said eccentric motion-producing means for translating said eccentric motion into a reciprocating motion of said end to periodically vary the resonance frequency of the chamber, and solenoid means to disengage said lever from said eccentric motion-producing means when the degree of energization of said solenoid is changed and to simultaneously shift said end to such a position that the natural resonance frequency of the chamber falls outside the range through which the resonance frequency may be periodically varied.

3. A testing system for an echo object locator of the type which transmits periodic pulses of electromagnetic energy subject to possible variation within a range of frequencies between a first frequency and a second frequency, said testing system comprising a resonator having a resonance chamber, an input circuit coupled to said resonator for supplying electromagnetic energy from said transmitted pulses to said resonance chamber, said resonator having a tuning plunger means adapted to tune the natural resonance frequency of said resonator to electromagnetic energy over a frequency range greater than the range between said first and second frequencies, a motor-driven means for producing an eccentric motion, a support, lever means pivotally mounted upon said support at one point and connected to said plunger means at a second point, said lever engaging said eccentric motion producing means at a third point for translating said eccentric motion into a reciprocating motion of said plunger means, the length of said lever from said one point to said second point being proportioned with respect to the length of said lever from said one point to said third point to reciprocate said plunger means over a sweep between a position whereat said resonator is tuned by said plunger means to said first frequency and a position whereat said resonator is tuned by said plunger means to said second frequency, and remotely controlled means connected to said lever to effectively disengage said lever from said eccentric motion producing means at will and to simultaneously shift said plunger meansto a position outside said reciprocating sweep.

WALTER F. KANNEENBERG.

JOHN P. KINZER.

CHARLES W. SCHRAMM.

IRA G. WILSON.

REFERENCES CITED The following references are of record in the file of this patent:

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